Fuel burner control system



July 9, 1968 A. G. METCALF ETAL. 3,391,984

FUEL BURNER CONTROL SYSTEM Filed March 13, 1967 United States Patent O 3,391,984 FUEL BURNER CGNTRL SYSTEM Arthur G. Metcalf and Philiip l1. Cade, Winchester, Mass.,

assgnors to Electronics Corporation of America, Cambridge, Mass., a corporation of Massachusetts Filed Mar. 3, 1967, Ser. No. 620,341 11 Claims. (Cl. 431-26) ABSTRACT F THE DSCLOSURE A solenoid plunger is utilized as a shutter interposed between the pilot burner and a radiation responsive flame sensor in a standing pilot type of gas installation.

The shutter is mounted within a housing on a plunger that has a hemsipherical shutter base portion of nonmagnetic material, a spacer disc of `magnetic material, a body of reduced diameter of magnetic material, and a guide at the other end of the body of magnetic material substantially the same configuration as the disc. A spacer member of non-magnetic material of substantially the same cross sectional configuration as the disc is interposed between the disc and the base member.

The shutter is opened if, in response to a demand for turn-on of the main burner the ame sensor gives a no flame indication. Should the Iflame sensor give a spurious frame present indication while the shutter is closed, the shutter is not opened and the vburner system is locked out. The valve furnishing fuel to the main burner is opened only if the flame sensor gives a flame present indication after the shutter 'is opened. This ensures that the main burner fuel supply cannot -be turned on without the presence of a pilot flame.

This invention relates to a fuel burner control system and more particularly to a protective safety system designed to prevent fuel from being supplied to the main burner when the pilot ame is not present.

It is 'a primary object of the invention to povide a novel and improved control system for a fuel burner of the standing pilot type `which prevents the supply of gas to a main vburner in a combustion chamber whenever a pilot ame is not present. Another object of the invention is to ensure that any failure of the pilot flame sensing device which could spuriously indicate the presence of a pilot flame when no pilot ame is in fact present is not permitted to initiate the turn-on of the fuel supply, but on the contrary such failue is itself rsensed and thereby prevents the fuel supply from being turned on. It is still another object of the invention to permit the turn-on and turn-off of the main burner to be controlled lby a thermostat or other conventional control means while .preserving the safety interlock feature of inhibiting such turn-on should the pilot flame be extinguished or should the sensing device fail to function properly.

Another object of the invention is to provide a novel and improved optical shutter configuration for use with a fuel burner control system. Y

The invention features in a `control system having a main burner, a conduit for supplying fuel to the main burner, a valve for controlling the flow of fuel through that conduit to the main burner, a pilot burner for igniting the main burner, a ame sensor for optically sensing the presence of the pilot burner flame, and a control for producing a request signal in response to a demand for heat, a shutter adapted to be interposed in the optical path between the pilot flame and the flame sensor, a control circuit for causing the shutter to open the optical path in response to the request signal provided that the optical scanner is not producing a ame 3,391,984 Patented July 9, 1968 present indication, and a further control circuit which opens the main burner fuel valve, after the optical path is opened, in response to a flame present signal from the fiame sensor. The invention provides a simple and reliable control for a standing pilot type of fuel burner.

In a particular embodiment, the shutter structure includes a cylindrical plunger component having a hemispherical bottom surface which is 'adapted to be moved under electromagnetic force between a position interposed in the optical path so that no sign significant amount of radiation from flame in the combustion chamber is sensed by the ame sensor to a position completely removed from that optical path. The plunger is lmovable within a cylindrical channel which is surrounded Iby a solenoid coil and includes a core of magnetic material. That core has a substantial length of reduced cross section so that a relatively large air gap in the magnetic circuit is provided when the shutter is in the closed position, which lair gap is reduced substantially when the shutter has been moved to the open position, thus reducing the amount of electrical energy required to hold the shutter in open position during operation of the main burner.

Other objects, features and advantages will be seen as the following description of a particular embodiment of the invention progress, in conjunction with the drawing, n which:

FIG. 1 is a diagrammatic view of a system incorporating the invention;

FIG. 2 is a detailed sectional view of the electromechanical shutter mechanism employed in the system shown in FIG. l; and

FIG. 3 is a schematic diagram of control for the system shown in FIG. 1.

Description 0f particular embodiment FIG. 1 shows a combustion chamber 10 in which is disposed `a main burner 12 which is supplied with gas fuel through conduit 14. An electromechanically operated valve 16 controls the fiow of fuel to main burner 12. A pilot burner 18 is fueled through conduit 20. Conduit 2t) branches off from conduit 14 upstream of valve 16 so that pilot ame 22 normally burns at all times regardless of whether valve 16 is open or shut. An optical path 24 penetrates the wall of chamber 10 at such a location that the light from pilot flame 22 irnpinges upon flame sensor 28, which may be of the type Shown in copending application Ser. No. 538,713, filed Mar. 30, 1966, in the name of Giuffrida et al. Normally closed electromechanically operated shutter structure 39 is interposed in optical path 24. A thermostat or similar control mechanism 32 operates in conjunction with electronic circuitry 33 to control the shutter mechanisrn 30 and to control the main burner fuel valve 16.

FIGURE 2 is an enlarged sectional view of the shutter mechanism 30. That mechanism includes a T-shaped coupling 40. the main leg of which defines a portion of optical path 24 and the right angle leg 42 of which defines an intersecting path in which a shutter plunger structure 44 is received. Riveted on leg section 42 is a solenoid coil support base 46 which receives solenoid coil 48. Also mounted on leg structure 42 is a cylindrical plunger housing 50 which is located at the center of coil 48. The plunger housing 50 has a stub portion 52 secured at its upper end Which includes an upwardly projecting threaded portion that receives a nut S4 to secure a housing cover `56 on the housing base 48. A disc spring washer 58 is interposed between cover 56 and coil 48 to firmly position coil 48 within the housing structure.

The plunger housing 50, in addition to stub 52, includes a tubular plastic member 60 having a ange 62 at its base which has formed on its upper surface an annular ridge 64 which is crushable during assembly of the housing base 46 to the leg portion 42 so that the housing 50 may be firmly and accurately positioned relative to coupling 40. Secured in the base of stub 52 is a shading slug in the form of a copper ring 66.

The plunger structure 44 includes a central body 70 of reduced diameter having sections 72, 74 at either end of further reduced diameter. A cup member 76, seated on the shoulder between body 70 and reduced end section 72, is secured in position by outward distortion of a portion of the metal of end section 72. A steel ring 78 is seated on the transition shoulder between body 70 and end section 74. Extension 74 has a series of teeth Y80 formed in it. The hemispherical base member 82 of the plunger structure includes a central tubular portion 84 which receives end section 74, teeth 80 distorting the wall of portion 84 to firmly secure base 82 to body 70. A tubular non-magnetic spacer 86 is positioned between cup 76 and disc 78. The magnetically conductive components of the plunger structure are body 70, the cup 76 and the disc 78. A spring 88 is received within cup 76 and `acts against housing stub 52 to normally K bias plunger structure downwardly to the dotted line position blocking the optical path 24 between the combustion chamber and the llame sensor.

It will be seen that in the energized position a relatively small air gap is provided between the disc 78 and the magnetic circuit including member 42 of the coil housing. In the de-energized position, this gap is substantially increased so that substantially more electrical energy is required to move the plunger 50 to open position than is required to hold it in that position.

A suitable control circuit is shown in FIG. 3. In that circuit, terminals 90, 92 are connected to a suitable source of power which is applied via transformer 94 to energize electronic circuitry 96 which responds to signal from sensor 28 and energizes llame relay coil 98. Also connected across secondary of transformer 74 is a series circuit of lockout switch actuator 100, normally closed contact 98-1 operated by tlame relay 98, a control relay coil 102, lockout contacts 100-1, and thermostat 32. The secondary winding of transformer 94 has a center tap at point 104 and normally open contacts 102-1 of the control relay are connected between tap 164 and the junction between llame relay contacts 98-1 and control relay coil 102. In the circuit between terminals 90, 92 and the primary winding of transformer 94 is connected shutter coil 48 and coil 106 which operates the main fuel valve 16. Normally open control relay contacts 102-2 are connected in the energizing circuit of both coils 48 and 106 while normally open fiame relay contacts 98-2 are connected in the energizing circuit of coil 106 alone. An auxiliary circuit of normally open flame relay contacts 98-3 and normally closed control relay contacts 102-3 is connected in parallel with the series circuit of contacts 984 and 102-1 so that if the flame relay 98 is in picked-up condition, due either to defective operation of that relay, of the electronics 96, or of sensor 28, an energizing circuit for lockout Vactuator 100 will be completed and that actuator will open contacts 100-1 to lockout the circuit and prevent opening the main valve 16.

In response to call for heat signalled by thermostat 32, a circuit is completed through lockout actuator 100, llame relay contacts 98-1, and lockout-contacts 100-1 to energize the control relay 102. Upon energization orig,I

control relay 102, contacts 102-1 close, completinga" in the combustion chamber 10. Upon such sensing of ame, relay 98 is energized, opening contacts 98-1 to terminate the heating of lockout actuator 100, and closing contacts 98-2 to open the main fuel valve 106.

Should the iiame in combustion chamber 10 for any reason become extinguished, this fact will be immediately indicated by sensor 28 and ame relay 98 will be deenergized, opening contacts 98-2. Contacts 98-1 Awill close and the system will be locked out after the predetermined time delay of lockout actuator 100.

When the thermostat 32 ends its call for heat, control relay 102 is de-energized, opening contacts 102-2 and de-energizing shutter coil 48 and main fuel valve coil 106. With the closing of the shutter, sensor 28 can no longer see flame and therefore llame relay 98 is deenergized. Thus the circuitry is reset in readiness for the next call for heat.

While a particular embodiment of the invention has* been shown and described, various modiiications thereof will be apparent to those skilled in the art. Therefore,I it is not intended that the invention be limited to theV disclosed embodiment or to details thereof and departures'jf may `be made therefrom lwithin the spirit and scope of` the invention as defined in the claims.

What is claimed is:

1. In a gas burner control system having a main, burner, a conduit for supplying gas to said main burner, a valve in said conduit for controlling the supply of gas to saidl main burner, an actuator for operating said valve, a piloti" burner for ignitinggas at' said main burner, a sensor fop; sensing the presence of flame at the pilot burner and pro-lviding a signal on sensing such flame, and a control for'j'l producing a request signal in response to a requirementf.

for heat, an optical shutter interposed between said pilot: burner and said sensor, a iirst control circuit for openin said shutter in response to said request signal, an inter lock circuit responsive to said sensor signal for preven ing the opening of said shutter if said sensor signal in dicates the presence of llame, and a second control circu for operating said actuator to open said gas supply valv in response to said sensor signal.

2. The apparatus as claimed in claim 1 wherein sai shutter includes structure deiining au optical path betwee said burner and said sensor and a barrier member adapte to be positioned in said path deiining structure to preven said sensor from sensing ame.

3. The apparatus as claimed in claim 2 wherein sai shutter includes a plunger member having a ferromag netic body'portion and a solenoid coil for acting on sai body portionto move said plunger relative to said pat delining structure.

4. The apparatus as claimed in claim 3 and further including structure biasing said plunger to a position interposed in said path dening structure.

5. The apparatus as claimed in claim 1 wherein said iirst control circuit includes a control relay for controlling said shutter and said second control circuit includes a flame relay for controlling said gas supply valve.

6. The apparatus as claimed in claim Y5 wherein said interlock circuit includes a contact controlled by said flame relay for preventing energization of said control relay to open said shutter when said ame relay is in llame presence indicating position.

7. The apparatus as claimed in claim 6 wherein said interlock circuit further includes a time delay relay for locking out the control system a predetermined time after either of said iiame and control relays but not both is in energized position.

8. The apparatus as claimed .in claim 7 wherein said shutter includes structure defining an optical path between said burner and said sensor and a barrier member adapted to be positioned in said path defining structure to prevent said sensor from sensing ilame. Y

9. The apparatus as claimed in claim 8 wherein said shutter includes a plunger member having a ferromagnetic body portion and a solenoid coil for acting on said body portion to move said plunger relative to said path defining structure.

10. The apparatus as claimed in claim 9 and further including structure biasing said plunger to a position interposed in said path defining structure.

11. The apparatus as claimed in claim 10 wherein said plunger member further includes an end portion of nonmagnetic material which is adapted to be interposed in said path defining structure and said body portion includes a section of reduced diameter so that a larger air gap between said coil and said body portion is present when said coil is de-energized than when said coil is energized 6 and said body portion is moved, and said shutter further includes a plunger housing of non-magnetic material having a shading slug disposed therein at one end of the housing.

References Cited UNITED STATES PATENTS 0 FREDERICK K ETTERER, Primary Examiner. 

